Locking Window Sash
Window sash lock
An excellent lock for window sash is to use two small, but strong, hinges one fastened on each side of the top sash close to the upper edge of the lower sash. This allows one wing of each hinge to swing freely which permits it to be swung over the upper edge of the lower sash, locking both securely. In placing the hinges in this position, they are out of sight and not in the way.